Piezoelectric needle selector in a circular knitting machine

ABSTRACT

A piezoelectric needle selector utilizes an upstanding knitting cylinder having a multiplicity of needle jacks mounted thereto for independent movement in a direction parallel to the axis of the knitting cylinder. A plurality of piezoelectric actuators, each having a stack of planar piezoelectric elements coupled at one end to a plunger, are mounted via respective holders to a fixed support frame disposed adjacent the knitting cylinder. The selective application of voltage pulses to the piezoelectric actuators results in the linear travel of the associated plungers toward and away from the knitting cylinder. The linear travel of the selected plungers is translated into the movement of the desired needle jacks up and down on the knitting cylinder, as by several needle select levers pivoted by the plungers and acting on the usual butts on the needle jacks.

BACKGROUND OF THE INVENTION

This invention relates to knitting machines and particularly to circularknitting machines for the production of stockings, socks and likegarments, possibly with the capability of creating patterns on theknitwear under electronic control. More particularly, the inventiondeals with a needle selector utilizing the piezoelectric effect forselectively actuating a multiplicity of needle jacks set on the surfaceof a knitting cylinder in such knitting machines

The piezoelectric needle selector is per se not new in the art and isdisclosed in Japanese Laid-Open Utility Model Publication No. 63-167187.This known device includes an upstanding knitting cylinder rotatablymounted on the machine frame and carrying a multiplicity of needle jacksslidably received in as many guideways cut longitudinally in itssurface. For selectively lifting the needle jacks on the revolvingknitting cylinder, the prior art needle selector employs pairs ofpiezoelectric actuators or elements each in the shape of a thin strip ofpiezoelectric material supported in a cantilever fashion. Each pair ofpiezoelectric elements have pairs of plungers on their free ends forengaging one end of one of several needle select levers which are eachmedially supported for pivotal movement about a horizontal axis. Eachneedle select lever terminates at the other end in a finger of extremelyhard alloy or ceramic material for acting on a butt of each selectedneedle jack on the knitting cylinder.

The knitting cylinder with the needle jacks thereon rotates at highspeed in the operation of the knitting machine. Electric pulses areimpressed to the piezoelectric elements as required by a desiredknitting pattern to be created. Each pair of piezoelectric elementsdeflect by resonance vibration in response to signals of the requiredresonance frequencies supplied to their anode and cathode. Suchresonance vibrations of the piezoelectric elements are imparted via theneedle select levers to the needle jacks and hence to the knittingneedles, causing the latter to travel up and down on the knittingcylinder. The desired pattern is thus formed on the fabric being knitted

The noted prior art device has proved to have certain shortcomings thatmust be overcome in order to establish true practical utility for thepiezoelectric needle selector. First, being made of very thin plates,the piezoelectric elements have been susceptible to destruction due tothe repeated application of stresses in use. They have also beenunsatisfactory in the length of the stroke over which the needle jacksare moved between the working and retracted positions on the knittingcylinder, and in the force under which they are retained in eitherposition Additionally, due to the lack of response and sufficiently highoperating speed, the known needle selector has been prone to chattering,resulting in imperfections in the patterns created.

SUMMARY OF THE INVENTION

The present invention seeks to eliminate all the listed shortcomings ofthe prior art

Briefly, the invention may be summarized as a piezoelectric needleselector in a circular knitting machine, comprising a knitting cylinderhaving an axis of rotation and having a multiplicity of needle jacksmounted thereto for independent movement in a direction parallel to theaxis of the knitting cylinder. In a position radially outward of theknitting cylinder, a plurality of plungers are supported by fixed holdermeans for independent linear movement toward and away from the knittingcylinder Also supported by the holder means are a plurality ofpiezoelectric actuators each comprising a horizontal stack of verticallyoriented, planar piezoeletric elements which is coupled at one end toone of the plungers. The selective application of a voltage to thepiezoelectric actuators results in the linear movement of the associatedplungers toward and away from the knitting cylinder. Means are providedfor translating the linear movement of the plungers into the movement ofthe needle jacks on the knitting cylinder.

The improved piezoelectric actuators of this invention, each comprisinga multiplicity of planar piezoelectric elements stacked together, arefar more durable and less susceptible to destruction than theconventional actuators each consisting of a single thin strip ofpiezoelectric material. The improved piezoelectric actuators offers theadditional advantage of providing a sufficiently long stroke of movementfor the needle jacks on the knitting cylinder.

The means for selectively moving the needle jacks up and down on theknitting cylinder in response to the movement of the plungers will bedisclosed herein in two primary different forms. Both forms are wellcalculated to achieve positive and quick needle selection withoutchattering and without imperfections in the fabric being knitted.

The above and other features and advantages of this invention and themanner of realizing them will become more apparent, and the inventionitself will be best understood, from a study of the followingdescription and appended claims, with reference had to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan, with parts shown in section for clarity, of thepiezoelectric needle selector embodying the principles of thisinvention;

FIG. 2 is a vertical section through the needle selector of FIG. 1;

FIG. 3 is a front or left hand end elevation of the needle selector ofFIG. 1;

FIG. 4 is a view somewhat similar to FIG. 2 but showing the needleselector on an enlarged scale in order to explain its operation;

FIG. 5 is an exploded perspective view of one pair of piezoelectricactuators and means associated therewith in the needle selector of FIG.1;

FIG. 5A is a vertical section showing one pair of piezoelectricactuators which are more improved than the piezoelectric actuators shownin FIGS. 4 and 5;

FIG. 6 is a fragmentary perspective view of a slight modification of theembodiment of FIGS. 1 through 5;

FIG. 7 is a horizontal section through a further preferred form ofpiezoelectric needle selector according to the invention;

FIG. 8 is an enlarged vertical section through the needle selector ofFIG. 7;

FIG. 9 is an exploded perspective view of one piezoelectric actuator andmeans associated therewith in the needle selector of FIG. 7;

FIG. 10 is an enlarged vertical section of cam means, shown togetherwith one representative needle jack, in the needle selector of FIG. 7;

FIG. 11 is a view similar to FIG. 10 except that the representativeneedle jack shown in a different position on the cam means;

FIG. 12 is an enlarged, fragmentary perspective view of the cam means ofFIGS. 10 and 11; and

FIG. 13 is a fragmentary perspective view of a slight modification ofthe embodiment of FIGS. 7 through 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first and in particular to FIGS. 1 and 2 an upstandingknitting cylinder 1 is mounted on a platform, not shown, of the knittingmachine for rotation about its own axis. The knitting cylinder 1 hasformed in its surface a multiplicity of groovelike guideways 2 extendingparallel to its axis. Slidably received in the guideways 2 are needlejacks 3, with butts 3a formed thereon, which are to be selectively movedup and down on the knitting cylinder 1 by means to be set forthhereafter. The up and down movement of the needle jacks 3 results in thesame movement of the usual knitting needles, not shown, of the machine.

As shown also in FIGS. 3 and 4, a generally rectangular support frame 4is mounted fast on a base B in the immediate vicinity of the knittingcylinder 1 for supporting the various working components of thepiezoelectric needle selector. The support frame 4 has a relativelythick backplate 6 to which there are firmly secured in a cantileverfashion a plurality of pairs of upper and lower holders 14 and 15 forpairs of piezoelectric actuators 17 and 18 constituting a feature of theinvention. The pairs of actuator holders 14 and 15 extend horizontallyin this embodiment or, speaking more broadly, in a direction at rightangles with the direction of the axis of rotation of the knittingcylinder 1.

FIG. 5 shows one such pair of upper and lower actuator holders 14 and 15together the piezoelectric actuators 17 and 18 housed therein and someother means directly associated therewith. It will be seen from thisfigure, as well as from FIGS. 1, 2 and 4, that each pair of actuatorholders 14 and 15 are adjustably movable relative to the support frame 4toward and away from the knitting cylinder 1 by the manipulation ofadjusting screws 16 on their ends projecting rearwardly of the backplate6.

The piezoelectric actuators 17 and 18 carried by these actuator holders14 and 15 are each of laminate construction, comprising a suitablenumber of vertically oriented, planar piezoelectric elements which arestacked into a horizontally extending pile of required length. Anapplication of voltage pulses to the piezoelectric actuators 17 and 18,through pairs of leads 17a and 18a, results in instantaneous changes inthe longitudinal dimension of the pile, as will be detailedsubsequently. The piezoelectric actuators 17 and 18 are controlled by anelectronic control system E (FIG. 5).

Coupled to the front ends, oriented toward the knitting cylinder 1, ofthe piezoelectric actuators 17 and 18 are plungers 19a and 19b ofcylindrical shape which are movable back and forth through guide holesin the front ends of the actuator holders 14 and 15. Each pair ofplungers 19a and 19b are to be thrust forwardly by the associated pairof piezoelectric actuators 17 and 18 into selective abutting engagementwith a pair of abutments 21a and 21b of one associated needle selectlever 21 yet to be described. The horizontal positions of the plungers19a and 19b with respect to the associated needle select lever 21 are tobe adjusted by the adjusting screws 16 for neat contact with theabutments 21a and 21b.

As will be noted from FIGS. 2, 4 and 5, each pair of actuator holders 14and 15 have magnets 20a and 20b of flat, square shape attached to theirfront ends for attracting the pair of abutments 21a and 21b of oneassociated needle select lever 21. It is therefore essential that atleast the abutments 21a and 21b of each needle select lever 21 be madeof magnetic material. The magnets 20a and 20b are centrally bored topermit the plungers 19a and 19b to loosely or slidably extendtherethrough and to project somewhat forwardly of the magnets. Driven bythe piezoelectric actuators 17 and 18, each pair of plungers 19a and 19bare to alternately push the pair of abutments 21a and 21b of one of theneedle select levers 21 through the magnets 20a and 20b.

Preferably, the plungers 19a and 19b should project approximately 0.10to 0.15 millimeter forwardly of the magnets 20a and 20b when thepiezoelectric actuators 17 and 18 are unenergized. Therefore, whenattracted to either of the magnets 20a and 20b, each needle select lever21 is held spaced as much distance from that magnet. This spacingcontributes materially to the quick, positive and chatter-free operationof the needle select levers 21 in response to the pushing action of theplungers 19a and 19b, as will become better understood as thedescription proceeds.

FIG. 2 best indicates a plurality of, eight in this embodiment, shaftsor pivot pins 22 rigidly supported at the front end of the support frame4. Each shaft 22 extends horizontally and all the shafts are containedin a vertical plane. Pivotally mounted to these shafts 22 are the notedneedle select levers 21 which function to convert the horizontalmovement of the plungers 19a and 19b into the vertical movement of theneedle jacks 3 on the knitting cylinder 1 Each in the shape of arecumbent T as seen in a side view as in FIG. 4, the needle selectlevers 21 have each the pair of abutments 21a and 21b on its rear end.Each pair of abutments 21a and 21b are formed at a suitable obtuse angleto each other for neat contact with the pair of plungers 19a and 19b ofone associated pair of piezoelectric actuators 17 and 18. It is thusseen that each needle select lever 21 pivots bidirectionally on one ofthe shafts 22 as the associated pair of plungers alternately push thepair of abutments 21a and 21b.

Each needle select lever 21 terminates at the other end in a finger 21cof suitable wear resistant material such as ultrahard alloys orceramics. The fingers 21c of the needle select levers 21 selectivelyengage the butts 3a of the needle jacks 3 with the pivotal movement ofthe needle select levers about the shafts 22.

Operation

The knitting cylinder 1 with the needle jacks 3 thereon rotates at highspeed in the direction of the arrow in FIG. 1 during the operation ofthe circular knitting machine. As stated before, the machine is equippedwith the electronic control system E for selectively energizing thepiezoelectric actuators 17 and 18 according to a desired design by whichthe knitwear is to be fashioned. Each selected pair of piezoelectricactuators 17 and 18 are to be alternately energized with electric pulsesignals.

Let us assume that a voltage pulse has just been impressed to onepiezoelectric actuator 17. Instantaneously translating this electricenergy into mechanical energy, the piezoelectric actuator 17 will extendby, say, 20 to 50 micronmeters. The piezoelectric actuator 17 onextension will impulsively thrust the associated plunger 19a toward theknitting cylinder 1. So thrust forwardly, the plunger 19a will push theabutment 21a of the associated needle select lever 21 against theattractive force of the magnet 20a. Since the other piezoelectricactuator 18 is now understood to remain unenergized, the needle selectlever 21 will pivot counterclockwise, as viewed in FIGS. 2 and 4, aboutthe shaft 22. Thereupon the finger 21c of the needle select lever 21will act on the butt 3a of one of the needle jacks 3 on the knittingcylinder 1.

It is self evident from the foregoing that the energization of the otherpiezoelectric actuator 18 of each pair of such actuators 17 and 18results in the pivotal movement of the associated needle select lever 21in a clockwise direction, as viewed in FIGS. 2 and 4. Thus, as the pairof piezoelectric actuators 17 and 18 are selectively activated asrequired by the preselected knitting design, the needle select levers 21will selectively act on the desired needle jacks 3, causing them totravel up and down on the knitting cylinder 1.

It is to be appreciated that the piezoelectric actuators 17 and 18 ofthe improved laminate construction according to the inventioninstantaneously extend in length in response to voltage pulses. Thedegree of extension is proportional to the original length to which theconstituent elements of each piezoelectric actuator is stacked.Consequently, the piezoelectric actuators can be easily constructed toassure a sufficiently long stroke for the longitudinal movement of theneedle jacks 3 between their working and retracted positions. Themechanical energy produced by the piezoelectric actuators 17 and 18 isalso far greater than that obtained from the conventional piezoelectricactuators each consisting of a single strip of piezoelectric material.These advantages of the improved piezoelectric actuators according tothe invention combine to realize speedy, accurate knitting operation byeach desired design.

Another pronounced advantage of the invention resides in the use of themagnets 20a and 20b in combination with the piezoelectric actuators 17and 18. These magnets are bored to permit the plungers 19a and 19b tonormally protrude from 0.10 to 0.15 millimeter or so forwardlytherethrough. Accordingly, when selectively attracted by the magnets 20aand 20b, the abutments 21a and 21b are nevertheless held spacedtherefrom, so that the needle select levers 21 can be readily pivoted ineither of the opposite directions when the plungers 19a and 19b arethrust forwardly by the piezoelectric actuators 18 and 19. This quickresponse of the needle select levers 21 leads to their positiveoperation without chattering.

Second Form

FIG. 5A illustrates a second form of the invention in which means forincreasing the stroke of the plungers 19a and 19b are provided.According to the second form, the actuator holder 14' has therein amovement multiplying device 30a between the piezoelectric actuator 17and the plunger 19a, and similarly the actuator holder 15' has therein amovement multiplying device 30b between the piezoelectric actuator 18and the plunger 19b.

The movement multiplying device 30a comprises a first vertical flexureelement 31a joined to the upper wall of the holder 14' by way of athinned portion, a second vertical flexure element 32a joined to thelower wall of the holder 14' by way of a thinned portion, and a thirdvertical flexure element 33a joined to the upper wall of the holder 14'by way of a thinned portion. The first flexure element 31a has a portion34a integrally joined thereto by way of a thinned portion to abut andhold the front end of the piezoelectric actuator 17. The first flexureelement 31a fixedly supports on the distal end thereof an abutting piece35a which is in slidable abutting engagement with the second flexureelement 32a. Similarly, the second flexure element 32a fixedly supportson the distal end thereof an abutting piece 36a which is in slidableabutting engagement with the third flexure element 33a. The rear end ofthe plunger 19a is fitted in the third flexure element 33a, and aresilient O-ring 37a is disposed between the element 33a and the frontwall of the holder 14'. The magnet 20'a is not of an annular shape inthis second form.

The movement multiplying device 30b comprises the same elements asdescribed above except that these elements are arranged symmetrically tothe elements within the holder 14' with respect to a horizontal planelying between the two holders 14' and 15'. The equivalent elementswithin the holder 15 are indicated with the same reference numerals witha subscript b instead of a.

When the piezoelectric actuator 17 is energized and extended, itsforward movement causes the first flexure element 31a to turn clockwiseas viewed, which in turn causes the second flexure element 32a to turncounterclockwise by way of the abutting piece 35a. In a similar way, thethird flexure element 33a is turned clockwise by way of the abuttingpiece 36a. Therefore, the plunger 19a is thrust forward a distancemultiplied by the device 30a because the device 30a functions to producea multiplied movement due to its leverage. The O-ring 37a serves to pushback the flexure elements when the piezoelectric actuator 17 isdeenergized. The same function is also obtained by the movementmultiplying device 30b. It will be understood that the movementmultiplying devices 30a and 30b ensure more rapid and reliable knittingoperation than those obtained by the foregoing embodiment.

Third Form

FIG. 6 illustrates a slight modification of the embodiment of FIGS. 1through 5. The modified needle selector features plates 23a and 23b ofsoft iron or like magnetic material attached respectively to the frontfaces of the magnets 20"a and 20"b on each pair of actuator holders 14"and 15". Each pair of magnets 20"a and 20"b exert their attractiveforces on the abutments 21a and 21b of the associated needle selectlever 21 through the magnetic plates 23a and 23b. The other details ofconstruction are as set forth above in connection with the embodiment ofFIGS. 1 through 5.

The magnetic plates 23a and 23b are intended to mitigate the effects ofthe magnetic fluxes due to the magnets 20"a and 20"b on the plungers 19aand 19b and hence to prevent the rebounding of the abutments 21a and21b. Experiment has proved that the magnetic plates 23a and 23b areeffective to assure more positive, chatter free operation of the needleselect levers 21.

Fourth Form

FIGS. 7 through 12 illustrate a third preferred form of piezoelectricneedle selector according to the invention, from which the needle selectlevers of the foregoing embodiments are eliminated for greatersimplicity in construction and greater reliability in operation.

As will be noted from FIGS. 7 and 8, the rotatable knitting cylinder 101of this embodiment has a tube 101a mounted concentrically therein. Amultiplicity of needle jacks 103, with butts 103a thereon, are slidablyengaged in respective groovelike guideways 102 defined longitudinally inthe surface of the knitting cylinder 101.

Disposed adjacent the knitting cylinder 101 is an elongate support frame104 immovably mounted on a fixed base B in an upstanding attitude. Thesupport frame 104 supports a series of piezoelectric actuators 117arranged one on top of another and in opposed relation to the knittingcylinder 101.

As will be best understood from a consideration of FIG. 9, thepiezoelectric actuators 117 are similar in construction to theircounterparts 17 and 18 of the foregoing embodiments, each comprising astack of planar piezoelectric elements laid horizontally within anactuator holder 114 and provided with a pair of leads 117a. All theactuator holders 114 are secured in a cantilever fashion to thebackplate 106 of the support frame 104. The horizontal positions of theactuator holders 114 are adjustably variable toward and away from theknitting cylinder 101 by adjusting screws 114a extending rearwardlytherefrom and nuts 116 thereon.

A plunger 119 is attached to the front end Of each piezoelectricactuator 117 and projects forwardly out of the front end of theassociated actuator holder 114. Each shown as a block of wear resistingmaterial for acting directly on the butts 103a of the needle jacks 103,the plungers 119 are movable back and forth relative to the actuatorholders 114 with the extension and contraction of the piezoelectricactuators 117. Such linear travel of the plungers 119 is guided by theactuator holders 114.

Also as in the foregoing embodiments, each actuator holder 117 has amagnet 120 of flat, square shape attached to its front end. The magnets120 of this third embodiment act, however, to attract the butts 103a ofthe needle jacks 103 on the knitting cylinder 101. It is thereforeessential that the needle jacks 103, or at least the butts 103a thereon,be made of magnetic material. The magnets 120 are centrally apertured topermit the plungers 119 to loosely or slidably extend therethrough andto project somewhat forwardly of the magnets. Driven by thepiezoelectric actuators 117, the plungers 119 are to push the butts 103aof the needle jacks 103 through the magnets 120.

As has also been stated in connection with the embodiment of FIGS. 1through 5, the plungers 119 should project the preferred distance of0.10 to 0.15 millimeter forwardly of the magnets 120 when thepiezoelectric actuators 117 are unenergized. The needle jack butts 103aare therefore to be held spaced as much distance from the magnets 120 bythe plungers 119 when attracted by the magnets. This spacing serve torealize the desired quick, positive and chatter-free process of needleselection by the piezoelectric actuators 117.

With reference to FIG. 8 a cam holder 130 is mounted fast under thetable B in fixed relation to a table 131. The cam holder 130 rigidlysupports on its inside edge an annular cam member 132 concentricallysurrounding the knitting cylinder 101.

As shown also in FIGS. 10 through 12, the annular cam member 132 has arim 133 erected along its outer edge. The rim 133 has a contoured topedge for relative sliding engagement with a cam follower butt 103cformed in a lowermost position on each needle jack 103. The contouredrim 133 of the cam member 132 serves as a lift cam for lifting theneedle jacks 103 on the knitting cylinder 101 upon rotation of thelatter.

Mounted fast in a preassigned angular position on the cam member 132 isa push cam 134 of arcuate shape disposed radially inwardly of the liftcam 133. The push cam 134 functions to push the bottom end portions ofthe successive needle jacks 103 radially outwardly of the knittingcylinder 101. The lift cam 133 lifts the needle jacks 103 as theirbottom end portions are pushed out by the push cam 134.

FIG. 8 indicates at 135 an L-shaped member rigidly mounted to theunderside of the support frame 104. This L-shaped member has a magnet136 and a magnetic plate 137 fastened thereto in a position opposite theknitting cylinder 101. The magnet 136 and magnetic plate 137 are forattracting an additional butt 103b formed on each needle jack 103 in aposition over the cam follower butt 103c, thereby aiding in theattraction of the needle jack butts 103a by the magnets 120 on the frontends of the actuator holders 114. The magnet 136 and magnetic plate 137may be omitted if the needle jacks can be smoothly attracted by themagnets 120.

Operation of Fourth

With the high speed rotation of the knitting cylinder 101 in theoperation of the circular knitting machine, the needle jacks 103 thereonwill have their bottom end portions pushed radially outwardly of theknitting cylinder as they slide over the push cam 134 in a positionopposite the vertical stack of piezoelectric actuators 117. The bottomend portions of the successive needle jacks 103 will thus be attractedby the magnets 120 on the front ends of the actuator holders 114 and bythe magnet 136 on the L-shaped member 135.

The piezoelectric actuators 117 may be selectively energized accordingto a desired knitting design. Operating in the same way as theircounterparts 17 and 18 of the foregoing embodiments, the piezoelectricactuators 117 on energization will impulsively thrust the plungers 120toward the knitting cylinder 101 thereby causing the plungers to pushthe butts 103a of the selected needle jacks 103 back into the guideways102 against the attractive forces of the magnets 120 and 136. The camfollower butts 103c of these needle jacks 103 will not ride on the liftcam 133, so that these needle jacks, and therefore the unshown knittingneedles associated therewith, will travel past the piezoelectricactuators 117 without being lifted on the knitting cylinder 101.

When not pushed back into the guideways 102 by the plungers 119, on theother hand, the needle jacks 103 will have their cam follower butts 103cforced onto the lift cam 133 by the action of both the push cam 134 andthe magnets 120 and 136. The needle jacks 103 with the associatedknitting needles will then be raised on the knitting cylinder 101. Thusthe fabric will be knitted to the desired design by the selectivelifting of the knitting needles on the knitting cylinder 101.

This needle selector gains some definite advantages because of theabsence of the needle select levers 21 of the foregoing embodiments. Asubstantial saving in time is realized in the operation of the needleselector as the plungers 119 of the piezoelectric actuators act directlyon the butts of the needle jacks. Let us assume that the knittingcylinder 101 carries 400 needle jacks and 400 knitting needles, and thatthe knitting cylinder rotates at the rate of 400 revolutions per minute.The absence of the needle select levers 21 has proved to result in asaving of time of approximately three milliseconds per needle. Thissaving of time, combined with the more positive, trouble-free operationof the needle selector, contributes materially to the greater productionof the knitting machine.

A further important advantage of this needle selector is that the numberof the piezoelectric actuators 117 in use can be reduced to one half ofthat of the piezoelectric elements 17 and 18 used in the embodiment ofFIGS. 1 through 5. The reduction of the number of the piezoelectricactuators accompanies, of course, a corresponding reduction in thenumbers of other parts associated therewith.

In this embodiment, too, as in all the other embodiments disclosedherein, the plungers 119 of the piezoelectric actuator 117 extendthrough the apertured magnets 120 and normally protrude therefrom by0.10 to 0.15 millimeter or so. Consequently, when attracted directly bythese magnets 120, the needle jack butts 103a are held spaced as muchdistance therefrom, so that they can be readily pushed away from themagnets by the plungers 119. The operation of this needle selector istherefore just as positive and chatter free as that of the firstdescribed embodiment.

Fifth Form

FIG. 13 illustrates a slight modification of the embodiment of FIGS. 7through 12. The modified needle selector has a plate 123 of soft iron orlike magnetic material attached to the front face of the magnet 120 oneach actuator holder 114, as in the modification of the FIGS. 1 through5 embodiment illustrated in FIG. 6. Each magnet 120 exert its attractiveforce on the butt 103a of each needle jack 103 through the magneticplate 123. The other details of construction can be as set forth abovein connection with the embodiment of FIGS. 7 through 12. As has beenstated with reference to FIG. 6, the magnetic plate 123 serves tomitigate the effects of the magnetic flux due to each magnet 120 on theassociated plunger 190 and hence to reduce chattering due to therebounding of the needle jack butts 103a.

It is, of course, understood that various modifications may be made inthe details of the above disclosed embodiments in order to conform tothe specific requirements of each application of the invention or todesign preferences, without departing from the scope of the invention.

What is claimed is:
 1. A piezoelectric needle selector in a circularknitting machine, comprising;(a) a knitting cylinder having an axis ofrotation and having a multiplicity of needle jacks mounted thereto forindependent movement in a direction parallel to the axis of the knittingcylinder, each of said needle jacks having a butt formed thereon; (b)holder means immovably supported in a position radially outward of theknitting cylinder; (c) a plurality of plungers supported by the holdermeans for independent linear movement toward and away from the knittingcylinder; (d) a plurality of piezoelectric actuators operativelysupported by the holder means and each comprising a stack of planarpiezoelectric elements which is coupled at one end to one of theplungers, whereby the selective application of a voltage to thepiezoelectric actuators results in the linear movement of the associatedplungers toward and away from the knitting cylinder; and (e) means fortranslating the linear movement of the plungers into the movement of theneedle jacks on the knitting cylinder, said translating meanscomprising: (f) a plurality of magnets attached to the holder means andeach apertured to permit one of the plungers to loosely extendtherethrough; (g) a plurality of needle select levers each mediallysupported for pivotal movement about an axis extending in a direction atright angles with the direction of the axis of the knitting cylinder;(h) a pair abutments of magnetic material formed on one end of eachneedle select lever so as to be alternately attracted by every twomagnets, each plunger when moved toward the knitting cylinder pushingone of the abutments away from one associated magnet, so that eachneedle select lever is pivoted bidirectionally by one pair ofpiezoelectric actuators; and (i) a finger formed on another end of eachneedle select lever for operative engagement with the butt of eachselected needle jack.
 2. The piezoelectric needle selector of claim 1wherein the plunger project a prescribed distance toward the knittingcylinder out of the apertures in the magnets when the piezoelectricactuators are unenergized, so that the abutments of the needle selectlevers are held spaced the prescribed distance from the magnets whenattracted thereby.
 3. The piezoelectric needle selector of claim 1further comprising a plurality of members of magnetic material attachedone to each magnet in order to mitigate the effects of magnetic flux dueto the magnets on the plungers.
 4. A piezoelectric needle selector in acircular knitting machine, comprising:(a) a knitting cylinder having anaxis of rotation and having a multiplicity of needle jacks mountedthereto for independent movement in a direction parallel to the axis ofthe knitting cylinder, each of said needle jacks having a butt formedthereon and being of magnetic material; (b) holder means immovablysupported in a position radially outward of the knitting cylinder; (c) aplurality of plungers supported by the holder means for independentlinear movement toward and away from the knitting cylinder; (d) aplurality of piezoelectric actuators operatively supported by the holdermeans and each comprising a stack of planar piezoelectric elements whichis coupled at one end to one of the plungers, whereby the selectiveapplication of a voltage to the piezoelectric actuators results in thelinear movement of the associated plungers toward and away from theknitting cylinder; and (e) means for translating the linear movement ofthe plungers into the movement of the needle jacks on the knittingcylinder, said translating means comprising: (f) a first cam for causingone end portion of each needle jack to move radially outwardly of theknitting cylinder during the rotation of the latter; (g) a plurality ofmagnets attached to the holder means in order to attract the butts ofthe needle jacks when the end portions of the needle jacks are movedradially outwardly of the knitting cylinder by the first cam, eachmagnet being apertured to permit one of the plungers to loosely extendtherethrough, the plungers when moved toward the knitting cylinderacting directly on the butts of the needle jacks and pushing their endportions back toward the knitting cylinder; and (h) a second cam forcausing those needle jacks whose end portions have not been pushed backtoward the knitting cylinder, to travel on the knitting cylinder in apredetermined direction parallel to its axis.
 5. The piezoelectricneedle selector of claim 4 wherein the plunger project a prescribeddistance toward the knitting cylinder out of the apertures in themagnets when the piezoelectric actuators are unenergized, so that theabutments of the needle select levers are held spaced the prescribeddistance from the magnets when attracted thereby.
 6. The piezoelectricneedle selector of claim 4 further comprising a plurality of members ofmagnetic material attached one to each magnet in order to mitigate theeffects of magnetic flux due to the magnets on the plungers.
 7. Thepiezoelectric needle selector of claim 1, further comprising movementmultiplying means provided between each piezoelectric actuator and eachplunger for transforming an extension of the piezoelectric actuator intoa multiplied linear movement of the plunger.
 8. The piezoelectric needleselector of claim 7, wherein the movement multiplying means comprisescantilever flexure elements extending transversely into the holder meansin a mutually parallel arrangement and in alternately oppositedirections, said flexure elements being in sliding contact through anabutting piece fixed to a distal end of an adjoining flexure element. 9.The piezoelectric needle selector of claim 8, further comprising aresilient O-ring interposed between the most forward flexure element anda front wall of the holder means.